Conventionally, a temperature sensor has been known which includes: a temperature sensing element including a temperature sensing portion, the electrical characteristics of which vary depending on temperature, and an electrode wire electrically connected to the temperature sensing portion; and a signal wire joined to the electrode wire. In the temperature sensor having the above structure, a platinum-rhodium (PtRh) alloy is used as a material of the electrode wire of the temperature sensing element.
The platinum-rhodium alloy has been known as a material excellent in processability, weldability, heat resistance, and corrosion resistance. The platinum-rhodium alloy has higher strength as compared to pure platinum having similar advantages, from room temperature to a high temperature, and is less worn by an oxidized vapor of iridium as compared to platinum-iridium (PtIr) alloy. Therefore, the platinum-rhodium alloy has been used as a heat-resistant alloy, a material for chemical equipment, a conductive material, a material for ignition electrodes, a contact material, and the like in a wide range of fields.
For example, Japanese Patent Application Laid-Open (kokai) No. 2003-261350 discloses platinum alloys including the platinum-rhodium alloy, as materials for forming glass fiber production nozzle and bushing. Japanese Patent Application Laid-Open (kokai) No. 2005-119959 indicates that the platinum-rhodium alloy is suitable for a glass ceramic material production apparatus. As described in these documents, the platinum-rhodium alloy is used as a high-temperature material having high resistance to oxidation.
Meanwhile, Japanese Patent Application Laid-Open (kokai) No. H11-40403 discloses a binary platinum-rhodium alloy wire incorporated in a temperature sensor element having heat resistance of 1000° C., and indicates that the content of Rh is desirably 10 to 20% by weight. Japanese Patent Application Laid-Open (kokai) No. 2010-60404 indicates that a platinum alloy containing 5 to 15 mass % of Ir and/or Rh is suitable as a material of an electrode wire of a temperature sensor used at high temperatures. As described in these documents, the platinum-rhodium alloy is favorably used also as a conductive material required to have heat resistance and high-temperature strength.